In the manufacture of packing containers of the type which comprise a container body and an end plate or the like made of a separate piece of material and attached to the container, the application of this loose end plate to the packing container body represents a stage in the manufacture. It is also possible for several loose end plates to be applied, e.g. when the packing container body is tubular and is to be provided with two end plates. The application and attachment of the loose packing container components can be done, of course, in a number of different ways, but it must be common to all, that after the components have been aligned in a correct mutual position the components are assembled and joined to one another by subjecting them to a greater or lesser joining pressure. The method of joining will depend, of course, on the type of material the components are made of.
In many different kinds of packing containers of the nonreturnable type, for e.g. food products, a packing material is used which wholly or partly consists of thermoplastic material. The thermoplastic material may possibly be in the form of outer layers of a laminated material which also comprises layers or other types of plastics, paper or aluminium foil. It is a common feature of such packing materials that they can be heat-sealed to one another by heating the required parts of the thermoplastic layers to a softening or sealing temperature, whereafter the parts are pressed together and allowed to cool while the compression continues.
The aforementioned type of seals between layers of thermplastic material will be very strong and liquid-tight, but in order to guarantee the desired liquid-tightness, even in the case of not wholly smooth material surfaces, a relatively large compression force is needed, which requires stoutly dimensioned heat sealing jaws, force application devices and machine frame. Difficulties in achieving a sufficiently large and uniform sealing force and a uniform and homogeneous heating are encountered also in packing containers of a geometric design which makes the sealing location not easily accessible, e.g. round or sharp-cornered packing containers of relatively small dimensions. On application of the profiled packing container components, e.g. end plates on sleeve-like packing container bodies, it is necessary, moreover, to preform the end plates so that they obtain the desired profile, e.g. with an edge embracing the edge of the packing container body. This also makes it necessary to ensure that prior to the application and sealing, the end plates and the packing container body are oriented and aligned accurately in relation to one another.